LTC (Long Thread Casing) is a conventional API standard casing connection defined by API Spec 5B, featuring an extended thread profile compared to STC (Short Thread Casing), which provides higher connection tensile strength at a slightly higher cost.
It uses 8-round threads per inch with a 60° thread angle and relies on thread compound for sealing rather than a metal-to-metal seal. LTC offers better tensile performance than STC but is still limited to moderate well conditions, typically used in medium-depth wells (3,000–5,000 meters) where higher axial loads are expected but extreme HPHT environments aren't a concern.
Looking for high-quality LTC threads compliant with API 5B? Click here to view our Mill Test Certificates (MTC).
LTC Thread specification
| Parameter | Specification / Value | Remarks |
| Thread Profile | Round Thread (8-Round) | Rounded crests and roots |
| Threads Per Inch (TPI) | 8 | Standard for API Round threads |
| Pitch (P) | 3.175 mm (0.125 inch) | Distance between thread peaks |
| Taper | 1:16 (0.0625 in/in) | 0.75 inch per foot on diameter |
| Included Angle | 60° | 30° flank angle on each side |
| Thread Height (h) | 1.810 mm (0.07125 inch) | Theoretical sharp thread height |
| Crest/Root Radius | 0.432 mm / 0.508 mm | Reduces stress and prevents galling |
LTC Coupling Dimensions (Reference Table)
Values are based on standard API 5CT specifications for common casing sizes.
| Casing OD (in) | Coupling OD (mm / in) | LTC Coupling Length (mm / in) |
| 4-1/2 | 127.00 / 5.000 | 177.80 / 7.000 |
| 5-1/2 | 153.67 / 6.050 | 203.20 / 8.000 |
| 7 | 194.46 / 7.656 | 228.60 / 9.000 |
| 9-5/8 | 269.88 / 10.625 | 266.70 / 10.500 |
| 13-3/8 | 365.12 / 14.375 | 273.05 / 10.750 |
Design and Geometry
Thread Profile: It is a "Round Thread" (V-shaped with rounded peaks and valleys). This design makes it easier to stab (align) and reduces the risk of cross-threading during installation.
Threads Per Inch (TPI): It typically has 8 threads per inch.
The "Long" Designation: The "Long" refers to the length of the threaded portion and the coupling. It has more thread engagement (more surface area touching) than its counterpart, the STC (Short Thread Coupled).
How it Seals
LTC threads do not have a dedicated metal-to-metal seal. Instead, the seal is created by:
Interference Fit: The threads are tapered, so they tighten as they are screwed together.
Thread Compound: A specialized grease known as "pipe dope" is applied to the threads. This compound fills the small gaps between the rounded crests and roots of the threads to prevent leaks.
Key Advantages
Strength: Because the coupling is longer and has more thread engagement, it offers better tensile strength (resistance to being pulled apart) than STC.
Leak Resistance: The additional threads provide a longer path for fluid to travel, which generally offers better leak resistance than STC under standard conditions.
Reliability: It is a proven, standardized design that is easy for crews to run and widely available globally.
Comparison to Other API Threads
LTC is part of the "Big Three" standard API casing connections:
STC (Short Thread Coupled): Same thread shape as LTC but shorter. It is used for shallower wells where the weight of the pipe string isn't as heavy. It is cheaper but weaker.
LTC (Long Thread Coupled): The middle ground. Used for medium-depth wells where higher tensile strength is needed.
BTC (Buttress Thread Coupled): Uses a trapezoidal (square-ish) thread shape. It is much stronger in both tension and compression than LTC and is used for very deep or horizontal wells.
When is it used?
LTC is most commonly used for casing in environments where:
The well is of medium depth.
There is moderate tension on the pipe string.
The pressure isn't so high that it requires "Premium" (gas-tight metal-to-metal) connections.
GNEE LTC Thread factory
GNEE LTC Thread Test equipments
GNEE LTC Thread certificate
FAQ
What is the difference between BTC and LTC threads?
The main differences between BTC (Buttress Thread) and LTC (Long Thread) can be summarized in three simple points:
1. Thread Shape (The Visual Difference)
LTC: Has Round threads (V-shaped with rounded peaks). It looks like a standard screw.
BTC: Has Trapezoidal threads (square/flat-topped). It looks like a staircase or a saw blade.
2. Strength (The Performance Difference)
LTC: Medium strength. It relies on the "wedging" of the round threads.
BTC: Much stronger. The flat thread face allows it to handle much higher tensile loads (pulling weight) and better resist "pull-out" failures in deep wells.
3. Application (Where to use them)
LTC: Used for medium-depth wells with standard weight loads. It is easy to screw together (make-up).
BTC: Used for deep, heavy, or horizontal wells. It is the preferred choice when the pipe string is very long and heavy, or when the pipe needs to be pushed/rotated into a horizontal section.
Can LTC threads be connected directly to STC or BTC threads?
LTC vs. STC: Even though they share the same thread profile (8-round), they have different thread lengths. Mixing them is strictly prohibited as it leads to connection failure or leaks.
LTC vs. BTC: Completely incompatible due to different thread shapes (Round vs. Trapezoidal).
What is the highest steel grade available for LTC?
LTC is most commonly used for J55, K55, and N80 grades. While it is available for P110, many engineers prefer BTC for P110 due to the higher tensile strength required in deeper wells.
